Multi-input and multi-output (MIMO) communication systems in which a transmission device and a reception device perform communication using an antenna array having multiple antennas have been known. Moreover, with the recent increase of communication band, communication using millimeter-waves has been considered to be applied. The millimeter-waves have large space propagation loss compared to electric waves of ultra-high frequency (UHF) band. Therefore, in the communication using millimeter-waves, the MIMO communication technique is applied to perform beam forming, thereby improving the communication quality.
Moreover, in the MIMO communication system, a wireless communication system in which a radio frequency (RF) precoding matrix including a phase shift relative to a transmission signal and a baseband precoding matrix to pre-code a transmission signal in a baseband are calculated has been known. In such a wireless communication system, a data signal having the number of data streams according to a rank acquired from a channel between a transmission device and a reception device is pre-coded by the calculated precoding matrix, and transmitted from the transmission device to the reception device. Related-art example is described in Japanese National Publication of International Patent Application No. 2014-526191.
When a data signal is transmitted from the transmission device with the number of data streams according to the rank, depending on a propagation environment between the transmission device and the reception device, the data signal received by the reception device can include many errors. In this case, retransmission of the data signal occurs frequently, and the throughput of data transmitted by the transmission device decreases. On the other hand, depending on a propagation environment between the transmission device and the reception device, a data signal can be received including a small number of errors by the reception device even if the data signal is transmitted with the number of data streams larger than the number of data streams according to the rank. However, as the number of streams is fixedly determined according to the rank, the throughput remains at a certain value, even though there is a possibility of improvement in the throughput.